Dielectric porcelain composition for electronic devices

ABSTRACT

A dielectric ceramic composition for electronic devices, which exhibits τf and ∈r characteristics equivalent or superior to those of the dielectric ceramic composition of the prior art, can inhibit the evaporation of Zn from the composition to thereby facilitate the control of makeup of the composition, can give homogeneous ceramics through short-time sintering more stably, is improved particularly in permittivity (Qf) and controllability of temperature characteristics, and permits downsizing of the dielectric elements. This composition is a solid solution of XBa(Zn ⅓ .Ta ⅔ )O 3 —Y(Ba Z .Sr 1−Z )(Ga ½ .Ta ½ )O 3  which contains a specific trivalent metal ion and has a Zn content adjusted to a predetermined level, wherein part of Ta contained in the XBa(Zn ⅓ .Ta ⅔ )O 3  moiety has been replaced by Nb. The composition is improved not only in permittivity by virtue of the above replacement but also in the degree of sintering by virtue of the above trivalent metal, i.e., Ga contained in the Y(Ba Z .Sr 1−Z )(Ga ½ .Ta ½ )O 3  moiety, thus attaining the effects of improvement in permittivity and control of temperature characteristics simultaneously.

This application is a 371 of PCJ/JP98/05524 filed on Dec. 4, 1998

TECHNICAL FIELD

The present invention relates to a dielectric ceramic composition forelectronic devices, that is, to improvements in a dielectric ceramiccomposition comprising a plurality of perovskite compounds used in theSHF bands, and more particularly to a dielectric ceramic composition forelectronic devices, into which specific trivalent metal ions areintroduced so as to control the Zn of the composition to a prescribedlevel, giving a ceramic with more homogenous internal properties andbetter sinterability, as well as a higher dielectric constant.

BACKGROUND ART

Dielectric ceramic compositions for various electronic devices, whichmake use of better temperature characteristics with lower loss of theproperties of the ceramic composition, include a variety of dielectricceramic compositions which are used in microwave strip line substratesand dielectric resonators such as for down convertors and satellitecommunications utilizing the lower loss of properties at the SHF bands,including temperature compensation capacitors.

Complex perovskite compounds of Ba(B_(⅓).A_(⅔))O₃ compositions (A: Ta,and B: divalent metal ions (Zn and/or one or more of Ni, Co, and Mn))are widely used in particular among conventional perovskite compounds asdielectric ceramic compositions generally employed in SHF bands.

The properties required of Ba(Zn_(⅓).Ta_(⅔))O₃ compositions used in theSHF bands, such as a higher ∈r, a high Q, and τf=0, are particularlystringent. The composition must be controlled to be meet suchproperties, and must therefore be sintered for long periods of times,such as for about 100 hours at 1500° C.

It is important to control the composition, particularly the Zn content,which tends to volatilize, in conventional dielectric ceramiccompositions. Zn also diffuses or spreads to the outside of the ceramicduring sintering, resulting in Zn-deficient components such asBa₅Ta₄O₁₅, which tend to form what is referred to as “skin,” making itdifficult to consistently obtain a ceramic with internal homogeneity, aswell as to obtain a ceramic with stable properties.

There is a particular need to adjust the resonance frequency temperaturecoefficient τf to a specific level according the application.Ba(Zn_(⅓).Ta_(⅔))O₃ is known to have a τf of around 0.

Research on the aforementioned Ba(Zn_(⅓).Ta_(⅔))O₃ composition in orderto control the Zn content in dielectric ceramic compositions withcomplex perovskite compounds has resulted in the proposal of aBa(Zn_(⅓).Ta_(⅔))O₃—YSr(Ga_(½). Ta_(½))O₃ solid solution systemcontaining specific trivalent metal ions and an XBa(Zn_(⅓).Ta_(⅔))O₃—Y(Ba_(Z).Sr_(1−Z))(Ga_(½).Ta_(½))O₃ solid solution system (JapaneseLaid-Open Patent Application (KOKAI) 2-285616 and Japanese Laid-Open PCTPatent Application (KOHYO) 7-102991).

The recent shifts to smaller electronic devices for communicationssystems and higher frequency bands in the communications field haveresulted in the need for greater dielectric elements because of thelower dielectric constant in conventional dielectric ceramiccompositions.

DISCLOSURE OF THE INVENTION

In view of the foregoing circumstances relating to conventional complexperovskite compounds, an object of the present invention is to provide adielectric ceramic composition for electronic devices which has a τf and∈r equal to or greater than that of conventional dielectric ceramiccompositions, but in which the volatilization of the Zn content of theceramic composition is controlled to make it easier to control thecomposition, to allow a ceramic with internal homogeneity to beconsistently be obtained upon sintering for shorter periods of time, toimprove the control of the dielectric constant Qf and temperatureproperties, and to make a smaller dielectric element.

As a result of extensive research to increase the dielectric constant ofXBa(Zn_(⅓).Ta_(⅔))O₃—Y(Ba_(Z).Sr_(1−Z)) (Ga_(½).Ta_(½))O₃ solid solutionsystems obtained by introducing specific trivalent metal ions andcontrolling the Zn content of a composition to a certain level, theinventors perfected the present invention upon finding that substitutinga portion of the Ta in the XBa(Zn_(⅓).Ta_(⅔))O₃ moiety with Nb canincrease the dielectric constant, that better sintering properties,which are an effect of the content of the aforementioned trivalentmetal, specifically, the Ga in the Y(Ba_(Z).Sr_(1−Z))(Ga_(½).Ta_(1/2))O₃system, are similarly obtained, and that a higher Qf and better controlof the temperature characteristics are also obtained.

As a result of further research on the aforementioned composition toadjust the resonance frequency temperature coefficient τf, the inventorsperfected the present invention upon finding that the resonancefrequency temperature coefficient τf could be selected as desired byvarying the ratio between Ba and Sr in the A site of complex perovskitecompounds.

That is, the present invention is a dielectric ceramic composition forelectronic devices, comprising a composition having a base compositionrepresented byXBa{Zn_(⅓).(Ta_(M).Nb_(1−M))_(⅔)}O₃—Y(Ba_(Z).Sr_(1−Z))(Ga_(½).Ta_(½))O₃where X, Y, Z, and M limiting the compositional range meet the followingvalues:X+Y=1; 0.3≦X≦1; 0.7≦Y >0; 0≦Z≦1; and 0.2 ≦M≦0.8.

BEST MODE FOR CARRYING OUT THE INVENTION

X and Y of the base composition formula are limited to 0.3≦X≦1 and0.7≧Y>0 in the present invention because when X is less than 0.3 and Yis greater than 0.7, the resulting dielectric ceramic compositionsuffers a considerable loss of Qf, and it becomes more difficult tocontrol the resonance frequency temperature coefficient.

Z in the base composition formula in the present invention is within therange of 0 to 1 so as to allow the resonance frequency temperaturecoefficient τf to be selected as desired within the range of +4.0 to−2.0 ppm/° C.

M in the base composition formula in the present invention is limited tothe range of 0.2≦M≦0.8 so as to allow the dielectric constant to beselected within the range of 29 to 35, and to be compatible according tothe size and connections of various filters and electronic devices. Avalue M of less than 0.2 results in a resonance frequency temperaturecoefficient deviating considerably from 0, whereas a value greater than0.8 fails to result in an improved dielectric constant.

In cases where the dielectric ceramic composition of the presentinvention is such that the Qf at 7 to 8 GHz is 90,000 to 160,000GHz,−2.0≦τf<+4.0 ppm/° C., and ∈r is 29 to 35, the properties will beequal to or greater than those of conventional dielectric ceramiccompositions, yet the volatilization of Zn contained in the dielectricceramic composition can be controlled to a certain extent, even duringsintering, to allow the composition to be more easily controlled, Znsegregation in the ceramic to be more easily prevented, a ceramic withbetter internal homogeneity to be more consistently obtained, and bettersintering properties to be obtained, which allow the manufacturing timeto be reduced.

In the present invention, virtually the same effects can be obtainedwhen the Zn is substituted by as much as 20 mol % divalent ions such asNi²⁺, Co²⁺, and Mn²⁺, or alkaline earth ions such as Ca²⁺ and Mg²⁺.

EMBODIMENT

Starting materials were measured out so as to give the compositionsshown in Tables 1-1, 2-1, and 3-1. The ingredients were wet mixed in aball mill, pre-fired for 2 hours at 1200° C., and then milled again to amean particle diameter of about 1 μm in the ball mill. The compositionsin Table 1-1 (Ta_(0.6).Nb_(0.4)), in Table 2-1 (Ta_(0.2).Nb_(0.8)), andin Table 3-1 (Ta_(0.8).Nb_(0.2)) were used as the base compositions.

The powders were molded by single screw compression molding at 1.0 to2.0 ton/cm² or by hydrostatic molding at a total pressure of 1 to 5tons, and then sintered at 1500 to 1550° C., giving sinters withdimensions of 9.8 mm φ×20 mm. The resulting sinters were cut to athickness of 4.5 mm or 9.0 mm. The specific dielectric constant ∈r at25° C. and 9 GHz, the Qf, and the resonance frequency temperaturecoefficient τf (ppm/° C.) were measured. The mean values of the resultsare given in Tables 1-2, 2-2, and 3-2.

The specific dielectric constant and the Qf in the tables were measuredusing a dielectric resonator based on the method of Hakki and Celeman.As such, the resonance frequency temperature coefficient τf, thedielectric constant, and the dielectric constant temperature coefficientτ∈ are related to the magnetic linear thermal expansion coefficient α asshown in the following formula.

τf=−½τ∈−α

The results in Tables 1-1 through 3-1 show that the dielectric ceramiccompositions according to the present invention are materials that havea broad resonance frequency temperature coefficient from −2.0 to around4 ppm/° C., little loss of properties, and a high dielectric constant.

TABLE 1-1 Composition XBa{Zn_(1/3).(Ta_(0.6).Nb_(0.4))_(2/3)}O₃-Y(Ba_(Z).Sr_(1−Z))(Ga_(1/2).Ta_(1/2))O₃ Sintering X Y Z conditionsEmbodiment 1 0.95 0.05 0.3 1500° C. × 2 Hr 2 0.95 0.05 0.5 1500° C. × 10Hr 3 0.95 0.05 1.0 1500° C. × 24 Hr 4 0.90 0.10 0.3 1500° C. × 2 Hr 50.90 0.10 0.5 1500° C. × 10 Hr 6 0.90 0.10 1.0 1500° C. × 24 Hr 7 0.700.30 0.5 1500° C. × 10 Hr 8 0.70 0.30 1.0 1500° C. × 24 Hr Comparison 90 1 0 1500° C. × 2 Hr 10 0 1 1 1500° C. × 2 Hr 11 1 0 0 1500° C. × 2 Hr12 1 0 1 1500° C. × 2 Hr

TABLE 1-2 Properties Specific dielectric Temperature constantcoefficient εr Qf (GHz) τf ppm/° C. Remarks Embodiment 1 33.4 156000+2.0 2 33.6 140000 +1.8 3 33.8 106000 +0.1 4 32.8 131000 +1.5 5 33.1140000 +1.2 6 33.4 145000 −0.2 7 31.9 160000 −0.1 8 32.3 158000 −1.3Comparison 9 27.3 86000 −45 10 26.4 42000 −51 11 32.8 64000 +1.0 Cracks12 33.1 38000 −2.1 Cracks

TABLE 2-1 Composition XBa{Zn_(1/3).Ta_(0.2).Nb_(0.8))_(2/3)}O₃-Y(Ba_(Z).Sr_(1−Z))(Ga_(1/2).Ta_(1/2))O₃ Sintering X Y Z conditionsEmbodiment 1 0.95 0.05 0.3 1500° C. × 2 Hr 2 0.95 0.05 0.5 1500° C. × 10Hr 3 0.95 0.05 1.0 1500° C. × 24 Hr 4 0.90 0.10 0.3 1500° C. × 2 Hr 50.90 0.10 0.5 1500° C. × 10 Hr 6 0.90 0.10 1.0 1500° C. × 24 Hr 7 0.700.30 0.5 1500° C. × 10 Hr 8 0.70 0.30 1.0 1500° C. × 24 Hr Comparison 90 1 0 1500° C. × 2 Hr 10 0 1 1 1500° C. × 2 Hr 11 1 0 0 1500° C. × 2 Hr12 1 0 1 1500° C. × 2 Hr

TABLE 2-2 Properties Specific dielectric Temperature constantcoefficient εr Qf (GHz) τf ppm/° C. Remarks Embodiment 1 33.9 120000+3.8 2 34.5 105000 +3.5 3 34.9 100000 +1.8 4 33.7 119000 +3.3 5 34.0109000 +2.9 6 34.2 110000 +0.9 7 32.5 129000 +0.9 8 33.5 126000 +0.1Comparison 9 27.3 86000 −45 10 26.4 42000 −51 11 33.6 41000 +3.1 Cracks12 83.7 39000 −1.6 Cracks

TABLE 3-1 Composition XBa{Zn_(1/3).(Ta_(0.8).Nb_(0.2))_(2/3)}O₃-Y(Ba_(Z).Sr_(1−Z))(Ga_(1/2).Ta_(1/2))O₃ Sintering X Y Z conditionsEmbodiment 1 0.95 0.05 0.3 1500° C. × 2 Hr 2 0.95 0.05 0.5 1500° C. × 10Hr 3 0.95 0.05 1.0 1500° C. × 24 Hr 4 0.90 0.10 0.3 1500° C. × 2 Hr 50.90 0.10 0.5 1500° C. × 10 Hr 6 0.90 0.10 1.0 1500° C. × 24 Hr 7 0.700.30 0.5 1500° C. × 10 Hr 8 0.70 0.30 1.0 1500° C. × 24 Hr Comparison 90 1 0 1500° C. × 2 Hr 10 0 1 1 1500° C. × 2 Hr 11 1 0 0 1500° C. × 2 Hr12 1 0 1 1500° C. × 2 Hr

TABLE 3-2 Properties Specific dielectric Temperature constantcoefficient εr Qf (GHz) τf ppm/° C. Remarks Embodiment 1 32.4 160000+1.5 2 32.7 158000 +1.4 3 32.7 159000 +0.5 4 31.5 141000 +1.0 5 31.9136000 +1.1 6 32.3 135000 −0.5 7 29.3 181000 −0.5 8 29.6 162000 −1.6Coparison 9 27.3 86000 −45 10 26.4 42000 −51 11 31.8 140000 −0.8 Cracks12 32.0 131000 −3.9 Cracks

INDUSTRIAL APPLICABILITY

In the dielectric ceramic composition for electronic devices in thepresent invention, a portion of the Ta in the XBa(Zn_(⅓).Ta_(⅔))O₃moiety of a XBa(Zn_(⅓).Ta_(⅔))O₃—Y (Ba_(Z).Sr_(1−Z))(Ga_(½).Ta_(½))O₃solid solution system is substituted with Nb, whereby the Qf at 7 to 8GHz is between 90,000 and 160,000 GHz, the resonance frequencytemperature coefficient ranges widely from −2.0 to around +4 ppm/° C.,and the ∈r is 29 to 35. This results in properties equal to or greaterthan those of conventional dielectric ceramic compositions. Because thevolatilization of the Zn in the ceramic composition is controlled to acertain extent, the composition is easier to control, Zn segregation inthe ceramic is easier to prevent, a ceramic with internal homogeneity ismore consistently obtained, better sintering properties, which are aneffect of the Ga in the Y(Ba_(Z).Sr_(1−Z))(Ga_(½).Ta_(½))O₃ system, arealso obtained, allowing the manufacturing time to be reduced, and inparticular a higher Qf and better control of the temperaturecharacteristics are also obtained. The material thus has lower loss anda higher dielectric constant.

What is claimed is:
 1. A dielectric ceramic composition for electronicdevices, comprising a composition having a base composition representedbyXBa{Zn_(⅓).(Ta_(M).Nb_(1−M))_(⅔)}O₃—Y(Ba_(Z).Sr_(1−Z))(Ga_(½).Ta_(½))O₃where X, Y, Z, and M limiting the compositional range meet the followingvalues: X+Y=1;0.3≦X<1;0.7≧Y>0;0≦Z ≦1; and 0.2≦M≦0.8.
 2. A dielectricceramic composition for electronic devices according to claim 1, whereinQf at 7 to 8 GHz is 90,000 to 160,000 GHz.
 3. A dielectric ceramiccomposition for electronic devices according to claim 1, wherein−2.0≦τf<+4.0 ppm/° C.
 4. A dielectric ceramic composition for electronicdevices according to claim 1, wherein the ∈r is 29 to
 35. 5. Adielectric ceramic composition for electronic devices according to claim1, wherein the Zn is substituted by as much as 20 mol % divalent metalion or alkaline earth ion.